<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
    content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <link rel="stylesheet" href="http://at.alicdn.com/t/font_1862466_s5gldd70lf.css">
</head>

<body>
  <div id="app"></div>
  <script>
    fnResize();
    window.onresize = function () {
      fnResize();
    }
    function fnResize() {
      var deviceWidth = document.documentElement.clientWidth || window.innerWidth;
      if (deviceWidth >= 750) {
        deviceWidth = 750;
      }
      if (deviceWidth <= 320) {
        deviceWidth = 320;
      }
      document.documentElement.style.fontSize = (deviceWidth / 7.5) + 'px';
    }
  </script>
</body>

</html>